1. Field of the Invention
Embodiments of the present invention relate to a photosensitive resin composition for a photoresist used in the fabrication processes of liquid crystal displays (LCDs), and a photoresist composition comprising the photosensitive resin composition. More particularly, embodiments of the present invention relate to a norbornene copolymer having an epoxy group, and a photoresist composition comprising the norbornene copolymer wherein the composition shows excellent mechanical and thermal properties, superior performance, including insulation, flatness, chemical resistance, etc., ease of pattern formation, high light transmittance, and is thus suitable for the formation of an interlayer insulating film of a device, such as an LCD or integrated circuit device.
2. Description of the Related Art
With the growing demand for liquid crystal display (LCD) panels, particularly, for use in television sets and monitors, glasses and panels are required to be large and to have high resolution, respectively. Under these circumstances, it is necessary to develop photoresists suitable for use in the relevant process conditions satisfying the requirement of glasses. Photo processes conducted on large-size glasses are critical in determining the line throughput and the physical properties of photoresist films, e.g., coating characteristics, spot-free, development contrast, resolution, adhesion to substrates, residual film characteristics and sensitivity, directly influence the quality of microcircuits formed in subsequent processes. Particularly, the sensitivity of photoresists produced during photo processes is an important factor affecting process tact of mass production lines and the high sensitivity of photoresists contributes to the improvement of productivity.
Resists for LDCs most widely used in the present photoresist market are positive-type systems composed of 2,1,5-diazonaphthoquinone (hereinafter, referred to as ‘DNQ’) and novolac resin, which undergoes photoreaction upon ultraviolet light irritation. The systems undergo a photoreaction due to the presence of DNQ upon being irradiated with light. DNQ is a compound which is insoluble in alkali before light exposure and becomes alkali-soluble upon light exposure. When the alkali-soluble DNQ is developed using an alkaline aqueous solution as a developer, exposed regions are dissolved. On the other hand, novolac resin is inherently alkali-soluble and reacts with the remaining DNQ under alkaline conditions to be crosslinked with the DNQ. Accordingly, the dissolution of the novolac resin is promoted due to the decomposition of the DNQ in exposed regions, but the dissolution of the novolac resin is hampered by the crosslinking between the DNQ and the novolac resin in unexposed regions. As a result, the shape of a mask is exposed during development. The DNQ functions to prevent the dissolution of the highly alkali-soluble novolac resin, and is thus called a “dissolution inhibitor”. Such systems are known to have an exposure sensitivity of about from 50 to 100 mJ/cm2. Higher sensitivity is still required for increased throughput and improved reactivity in LCD fabrication processes. To this end, the concept of chemical amplification has been introduced.
Chemically amplified photoresists are comprised of a photoacid generator (PAG) and a polymer combined with a dissolution inhibitor. When the chemically amplified photoresists are exposed to light, the dissolution inhibitor bonded to the skeleton of the polymer is hydrolyzed by the catalytic action of acid generated from the photoacid generator, causing a modification in the polarity of the polymer. The development of the polarity-modified polymer using a polar or non-polar solvent leads to the formation of a positive- or negative-type photosensitive film pattern. As a resin most applicable to these chemically amplified photoresists, a polyvinylphenol protected by a t-butoxycarbonyl group is disclosed in U.S. Pat. No. 4,991,628.
Interlayer insulating films are used to insulate wirings arranged in respective layers of TFT-type liquid crystal displays or integrated circuit devices. The use of photosensitive materials with a small number of processes and superior flatness are required for the production of interlayer insulating films in the shape of desired patterns. The structure of TFT-type liquid crystal display devices varies with an increase in the definition of liquid crystal displays (LCDs). For example, interlayer insulating films often have a large thickness due to their poor insulating properties, but they are required to have improved flatness before use.
However, when photosensitive resin compositions as interlayer insulating films have a large thickness, the transparence of the compositions is inevitably deteriorated with increasing thickness of the films.